1. Field of Invention
The present invention relates to a navigation apparatus for a vehicle and a storage medium that search for a new route during a route guidance.
2. Description of Related Art
To quickly search for a route from a place of departure to a destination, navigation apparatuses of the related art have previously stored map data hierarchized according to the degree of details of roads from upper-rank main roads (such as expressways, superhighways, toll roads and national roads) to lower-rank ordinary roads, and searched routes near the place of departure and near the destination in lower-rank roads or searched routes from an intermediate point between the place of departure and the destination in upper-rank roads.
The route searching method of the related art performs route searching by considering only those roads in the vicinity of the place of departure and the destination. The method therefore searches only for upper-rank main roads stored at a midway point between the place of departure and the destination, though there may be lower-rank ordinary roads at the same midway point which are shorter routes to a destination. The methods of the related art may therefore guide one to a route having a longer way to the desired destination. Even in the case where there is a shorter way by an ordinary road, as indicated by a thin line in FIG. 9, for example, a longer national road, as indicated by a thick line in FIG. 9, is searched and guided as an optimal route according to the previous methods.
Accordingly, it is an object of the invention to prevent guidance of a longer route to a desired destination from a midway point between the place of departure and the destination by searching for a route using all road data, i.e., upper-rank and lower-rank road data, every predetermined time or every predetermined distance traveled.
According to the invention, there is provided a navigation apparatus for a vehicle that searches for a route to a destination and gives guidance, the navigation apparatus comprising a present-location detecting means for detecting a present location of a mobile body; an information storage means which holds information necessary for route searching including map data hierarchized, or layered, according to the degree of details of roads from upper-rank main roads to lower-rank ordinary roads; a route searching means that searches for a route based on present-location information detected by the present-location detecting means and the map data stored in the information storage means; an output means for outputting route information searched by the route searching means; and a control means for outputting the route information to the output means, whereby the route searching means searches for an optimal route from a present location to a destination based on the map data every predetermined time or every predetermined distance.
According to the invention, there is also provided a storage medium incorporating a program capable of detecting a present location of a mobile body; searching for a route to a destination based on map data hierarchized, or layered, according to the degree of details of roads from upper-rank roads to lower-rank roads; and outputting information of the searched route, whereby the program searches for an optimal route from a present location to a destination based on the map data every predetermined time or every predetermined distance.